TAMR is expected to be one of the future generations of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to near its Curie temperature where both of its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. In TAMR, optical power from a light source is converted into localized heating in a recording medium during a write process to temporarily reduce the field needed to switch the magnetizations of the medium grains. Thus, with a sharp temperature gradient of TAMR acting alone or in alignment with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head also typically includes an optical waveguide (WG) and a plasmon antenna (PA) or plasmon generator (PG). The waveguide serves as an intermediate path to guide the external laser light to the PA or PG where the light optical mode couples to the local plasmon mode of the PA or to the propagating plasmon mode of the PG. After the optical energy is transformed to plasmon energy, either with local plasmon excitation in the PA or with energy transmission along the PG, it is concentrated at the medium location where heating is desired. Ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance.
However, in the prior art, alignment has been difficult to achieve and the spot size is typically around 100 nm or greater which is significantly larger than the <50 nm size needed to make the first generation of TAMR devices with high optical efficiency.
Current technology encompasses a TAMR head structure that integrates an edge plasmon generator (EPG) with a triangular shape from a cross-sectional view. The shape edge of the triangular EPG is placed in the vicinity of an optical waveguide and supports a very confined edge plasmon mode. Through evanescent coupling, the optical energy in the WG can be efficiently transferred to EPG mode. The EPG transmits the plasmon energy toward the air bearing surface (ABS) and focuses the energy at a spot on the medium located underneath the EPG. The local confinement of the edge plasmon mode is determined by the angle that forms the shape edge of the EPG, the radius of the triangle corner, the noble metal composition of the EPG, and the dielectric material surrounding the tip. For a 25 nm tip radius, optical spot size in the medium is about 100 nm in full-width half maximum. By using a plasmon shield formed proximate to the EPG tip at the ABS as described in related U.S. Pat. No. 8,036,069, the optical spot on the medium can be further reduced. Optical spot size with a plasmon shield is related to the gap distance between EPG and plasmon shield and can be reduced to 50 nm with a gap distance less than 40 nm, for example. While the optical spot size may be reduced to a range of 20-30 nm with a 10 nm gap distance, the optical efficiency is significantly lowered which requires a higher laser power. However, higher laser power is not desirable for various reasons including reliability concerns.
Current technology does not provide a TAMR structure with a PG that allows for a narrow optical spot size of around 20 nm or less without requiring a high laser power, and where the PG can be fabricated with a good tolerance necessary for a high yielding manufacturing process. Furthermore, a plasmon generator is needed to enable scalable spot size to support areal density growth with good reliability.